Author: rstone
Date: Tue Sep 7 00:23:45 2010
New Revision: 212281
URL: http://svn.freebsd.org/changeset/base/212281
Log:
In munmap() downgrade the vm_map_lock to a read lock before taking a read
lock on the pmc-sx lock. This prevents a deadlock with
pmc_log_process_mappings, which has an exclusive lock on pmc-sx and tries
to get a read lock on a vm_map. Downgrading the vm_map_lock in munmap
allows pmc_log_process_mappings to continue, preventing the deadlock.
Without this change I could cause a deadlock on a multicore 8.1-RELEASE
system by having one thread constantly mmap'ing and then munmap'ing a
PROT_EXEC mapping in a loop while I repeatedly invoked and stopped pmcstat
in system-wide sampling mode.
Reviewed by: fabient
Approved by: emaste (mentor)
MFC after: 2 weeks
Modified:
head/sys/vm/vm_mmap.c
Modified: head/sys/vm/vm_mmap.c
==============================================================================
--- head/sys/vm/vm_mmap.c Mon Sep 6 23:52:04 2010 (r212280)
+++ head/sys/vm/vm_mmap.c Tue Sep 7 00:23:45 2010 (r212281)
@@ -579,6 +579,7 @@ munmap(td, uap)
* Inform hwpmc if the address range being unmapped contains
* an executable region.
*/
+ pkm.pm_address = (uintptr_t) NULL;
if (vm_map_lookup_entry(map, addr, &entry)) {
for (;
entry != &map->header && entry->start < addr + size;
@@ -587,16 +588,23 @@ munmap(td, uap)
entry->end, VM_PROT_EXECUTE) == TRUE) {
pkm.pm_address = (uintptr_t) addr;
pkm.pm_size = (size_t) size;
- PMC_CALL_HOOK(td, PMC_FN_MUNMAP,
- (void *) &pkm);
break;
}
}
}
#endif
- /* returns nothing but KERN_SUCCESS anyway */
vm_map_delete(map, addr, addr + size);
+
+#ifdef HWPMC_HOOKS
+ /* downgrade the lock to prevent a LOR with the pmc-sx lock */
+ vm_map_lock_downgrade(map);
+ if (pkm.pm_address != (uintptr) NULL)
+ PMC_CALL_HOOK(td, PMC_FN_MUNMAP, (void *) &pkm);
+ vm_map_unlock_read(map);
+#else
vm_map_unlock(map);
+#endif
+ /* vm_map_delete returns nothing but KERN_SUCCESS anyway */
return (0);
}
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